Low cost digital microphones include a biasing circuit followed by an analog-to-digital converter. The competitiveness of a microphone is mainly given by its performance (power consumption, dynamic range, resolution, as well as other performance features) and its cost (silicon area, package size vs. sensitivity, as well as other cost drivers). Sigma Delta ADCs currently available have been pushed to technology limits and market trends require innovative solutions. VCO-based ADCs are promising alternatives to the conventional voltage encoding-based circuits. For a VCO-ADC built with a multiphase Ring Oscillator (“RO”), the area and power consumption of the quantization circuitry can be reduced with a coarse-fine quantization architecture, using a counter for the integer phase progression (multiples of 2π), and a fine quantization for the fractional part of the phase progression. However, errors resulting from the desynchronization between the coarse and the fine phase estimations, and those caused by direct sampling of the phases, may compromise the ADC performance.